Global demand for clean fuels, such as ultra-low-sulfur-diesel (ULSD), has risen quickly because many environmental regulations have been established to substantially lower the sulfur levels of fuels in order to reduce sulfur dioxide (SO2) emissions from use of such fuels.
Hydroprocessing processes have been used to treat hydrocarbon feeds to produce clean fuels. Such processes include hydrodesulfurization (HDS) and hydrodenitrogenation (HDN), which remove sulfur and nitrogen, respectively, from the feeds.
Conventional hydroprocessing processes use trickle bed reactors, in which hydrogen is transferred from a vapor phase through a liquid phase hydrocarbon feed to react with the feed at the surface of a solid catalyst. Thus, three phases (gas, liquid and solid) are present. Trickle bed reactors are expensive to operate and require large quantities of hydrogen, much of which must be recycled through expensive hydrogen compressors. Heat removal from the highly exothermic hydroprocessing processes is inefficient. Significant coke forms on the surfaces of catalysts in trickle bed reactors, causing catalyst deactivation.
Ackerson, in U.S. Pat. No. 6,123,835, discloses a two-phase hydroprocessing system which eliminates the need to circulate hydrogen through the catalyst. In the two-phase hydroprocessing system, a solvent or a recycled portion of hydroprocessed liquid effluent acts as diluent and is mixed with a hydrocarbon feed. Hydrogen is dissolved in the feed/diluent mixture to provide hydrogen in the liquid phase. All of the hydrogen required in the hydroprocessing reaction is available in solution.
Petri, in U.S. patent application with Pub. No. US 2010/0326884, discloses a hydroprocessing process utilizing staged hydroprocessing reaction zones. Petri discloses that at least the initial reaction zone is a substantially three-phase hydroprocessing zone. Petri also discloses that a hydrocarbon feed is divided into portions, and a portion of untreated fresh feed mixed with a treated effluent is supplied to each reaction zone. The above treated effluent acts as a diluent and hydrogen source.
It is desirable to have a process for hydroprocessing hydrocarbon feeds in a smaller and simpler system with a reduced recycle ratio and enhanced sulfur and nitrogen conversion. It is also desirable to have a process for hydroprocessing to produce clean fuels with multiple desirable properties such as low density and high cetane number.